Gear Ratio & Tire Size Options For A D600??

Posted By: E-Ticket

Gear Ratio & Tire Size Options For A D600?? - 07/04/14 12:35 AM

ok.......so I have this 1974 D600 with a 361, 4-speed + 2 speed rear axle that I bought originally to do some scrap & crap hauling and have also considered converting it to a car hauler because its absolutely perfect for such a project due to the need for "stretching" the frame is not required on this one....just add some length to the end of the rails and your golden...... I do have it currently for sale here on Moparts but if it does not sell soon, rather than let it sit, I am still considering the ramp bed conversion?

Two things that I would have to consider changing if the options are available is to maybe change the rear end gear ratio to a higher gear and would like to put a smaller diameter wheel & tire on it OR instead of changing the rear center section out for higher gears....maybe change it over to a 5-speed or 6-speed transmission??

My questions are.....does anyone know what if any higher gear ratio gear options are available and also....how much smaller of this type of wheel & tire can I put on it in order to lower the truck closer to the ground? It currently has 9.00 x 20 tires and I believe the rear ratio is a 5:57/7:60 in an Eaton Planetary Spiral Bevel type rear end.

Attached picture 8196596-I.jpg

Posted By: CTD5.9

Re: Gear Ratio & Tire Size Options For A D600?? - 07/04/14 04:45 PM

I am currently trying to do the something similar with one. In my case I am putting a club cab and a flat deck on and using it to tow a big goose neck. Mine is getting a 5.9 cummins so I need to get the rpms down, I have not for the life of me been able to find different gear sets for that diff. I have began the search for an auxilary transmission though, either a spicer or brown-lipe with an over drive in it.

As for tires the 20's are fairly out dated, I think 22.5's are fairly common. There are some lower profile ones out there but I am not sure how the rims would work on the trucks dayton system.

Posted By: finn

Re: Gear Ratio & Tire Size Options For A D600?? - 07/07/14 09:09 PM

19.5 rims are popular with "LoPro" medium trucks, but I see the truck you pictured has the old Dayton style hubs and rims.

You would have to switch your axles out to hub piloted Budds from a later truck. That would get you better (Disc) brakes, although all of the recent trucks have antilock systems which is a further complication.

Unless you can pick up a decommissioned school bus donor cheap, you may want to just enjoy the old girl for what she is: a 50 mph local hauler.

Posted By: E-Ticket

Re: Gear Ratio & Tire Size Options For A D600?? - 07/08/14 10:14 PM

Quote:

I am currently trying to do the something similar with one. In my case I am putting a club cab and a flat deck on and using it to tow a big goose neck. Mine is getting a 5.9 cummins so I need to get the rpms down, I have not for the life of me been able to find different gear sets for that diff. I have began the search for an auxilary transmission though, either a spicer or brown-lipe with an over drive in it.

As for tires the 20's are fairly out dated, I think 22.5's are fairly common. There are some lower profile ones out there but I am not sure how the rims would work on the trucks dayton system.

That is what I am running into also as far as not finding info. on optional gear sets......thanks!!!

Posted By: E-Ticket

Re: Gear Ratio & Tire Size Options For A D600?? - 07/08/14 10:20 PM

Quote:

19.5 rims are popular with "LoPro" medium trucks, but I see the truck you pictured has the old Dayton style hubs and rims.

You would have to switch your axles out to hub piloted Budds from a later truck. That would get you better (Disc) brakes, although all of the recent trucks have antilock systems which is a further complication.

Unless you can pick up a decommissioned school bus donor cheap, you may want to just enjoy the old girl for what she is: a 50 mph local hauler.

yeah....reality is setting in on a few things unless I want to just change out everything like the drivetrain over to a 12 valve with a 6-speed and change the rear end also..... Not sure I am that excited about changing this much for the purpose??

I have got this "big girl" up over 60 mph fairly easy so its not so horrible the way she is now.....

Posted By: SteveS

Re: Gear Ratio & Tire Size Options For A D600?? - 07/08/14 10:59 PM

I had an F600 of about the same vintage (1978). It had a wide ratio 5-speed, with a single speed rear. It had 22.5" tubeless steel wheels, with somewhat lower profile tires. It would cruise pretty well at 70.

Posted By: dogdays

Re: Gear Ratio & Tire Size Options For A D600?? - 07/15/14 06:15 PM

First of all do you understand that making the tires smaller diameter increases the rpm at 60? So going smaller on the tires and to a higher speed rear would work against each other.

I'd start looking for an auxiliary transmission to go behind whatever transmission you end up with.

Or use something like a late model car 6-speed with 0.50 Sixth gear.

R.

Posted By: finn

Re: Gear Ratio & Tire Size Options For A D600?? - 07/17/14 03:58 AM

A car transmission means you loose the transmission mounted parking brake of the medium truck. Also, the first gear ratio would be too high to get the thing rolling when loaded.

The truck probably has a SAE type bellhousing & mounting system too.

Posted By: dogdays

Re: Gear Ratio & Tire Size Options For A D600?? - 07/17/14 11:12 PM

http://www.olddodges.com/dseries.htm
has as good of information as I found online.

The D600 used an NP435 transmission as the standard, although a couple of five-speeds were available. Engines were 318 and 361, and clutches were 12" with 13" optional.
The gasoline engines did not use SAE bellhousings.

R.

Posted By: E-Ticket

Re: Gear Ratio & Tire Size Options For A D600?? - 07/19/14 06:32 PM

Quote:

http://www.olddodges.com/dseries.htm
has as good of information as I found online.

The D600 used an NP435 transmission as the standard, although a couple of five-speeds were available. Engines were 318 and 361, and clutches were 12" with 13" optional.
The gasoline engines did not use SAE bellhousings.

R.

thanks.....I saw that link also and it is a strong wealth of information!

If I do ever get the chance to make a change, it will most likely be for a 5 speed with this motor or a 6-speed with a 12 valve CTD??

Posted By: Handygun

Re: Gear Ratio & Tire Size Options For A D600?? - 07/19/14 08:26 PM

The 22.5 Dayton hoops will fit your drums, the np-540 is direct in top just like the 435. A Dodge CTD is a neat idea but what a can of worms that opens up ie parking drum and transmissions with overdrive. There are 2 D-600's heavy and light. the last one I had weighed 9900 empty. it was a 197wb, Daytons, 24k gvw,same drive train as yours 16ft flatbed. Put 5 tons of scrap on there and that asking a lot out of a Getrag.

Posted By: E-Ticket

Re: Gear Ratio & Tire Size Options For A D600?? - 08/08/14 07:46 AM

ok.....anyone ever taken a truck this size and changed the chassis down to a D300, 1 Ton Chassis??

Posted By: CTD5.9

Re: Gear Ratio & Tire Size Options For A D600?? - 08/08/14 04:09 PM

The cabs are the same, with just taller mounts to raise it up. I am not sure about the rest of it mounting onto a 1 ton frame

Posted By: E-Ticket

Re: Gear Ratio & Tire Size Options For A D600?? - 08/08/14 04:19 PM

If I had at least a D100 or D200 to sit next to it, I could at least compare them side by side and do some measuring but I don't........

Posted By: QuickDodge

Re: Gear Ratio & Tire Size Options For A D600?? - 08/10/14 04:35 AM

Thanks for the pictures of your truck. It looks like a great old truck!

Many years back, a knowledgeable Dodge truck guy told me there were a FEW overdrive 5 speeds used in the medium duty trucks. Unfortunately, most of the 5 speeds were direct drive in 5th gear though. Attempting to locate one of these rare overdrive transmissions might be nearly impossible. Of course, locating accurate information on such an unusual truck probably is not real easy either!

I wonder if a transmission out of another brand of truck would bolt up to the bellhousing in your truck?

Posted By: E-Ticket

Re: Gear Ratio & Tire Size Options For A D600?? - 08/10/14 06:41 PM

probably so because like in the 1994-2002 model 5-speeds, Dodge and Chevrolet shared the same transmission in the 2500 & 3500 trucks with the input shaft being the main difference.

Posted By: WO23Coronet

Re: Gear Ratio & Tire Size Options For A D600?? - 08/10/14 10:44 PM

What about a GV Overdrive unit? You'd have to mount it after the drum brake but do you think it would work? I think they're a .75 gear ratio, supposed to be very strong, used alot in RV's

Posted By: E-Ticket

Re: Gear Ratio & Tire Size Options For A D600?? - 08/10/14 11:02 PM

That is a thought..... I currently have the truck for sale but part of me does not want to turn loose of it and would seriously like to retain most of its originality for nostalgic reasons. Would like to change it over to a race car hauler or an enclosed race car hauler like back in the day when they were widely used.

Our local track is 41 miles each way so it would be tough to justify a CTD change over other than the fact that it would be cool as hell to rumble through the gates at the track with a 12 valve under the hood.....

Have been using it a lot lately to haul junk and tree limbs, etc to the dump and it is excellent for that but it tops out at about 60 mph. Would like to make it run 80 mph with ease so that I could drive it at 70 mph with out making it work for it......

Posted By: WO23Coronet

Re: Gear Ratio & Tire Size Options For A D600?? - 08/11/14 05:03 AM

What kind of RPM are u turning at 60 MPH?

Posted By: E-Ticket

Re: Gear Ratio & Tire Size Options For A D600?? - 08/11/14 05:12 AM

Quote:

What kind of RPM are u turning at 60 MPH?

don't know....funny you ask....I was just thinking about that yesterday when I had it out for a dump run. Should have wired up a tach by now but just never did.

Posted By: Handygun

Re: Gear Ratio & Tire Size Options For A D600?? - 08/13/14 12:41 AM

Trying to find a different center section out of a different truck could work as a whole other brake to brake out of different truck. Most med duty's (exc [Edited by Moparts - Family Friendly Site - Keep it clean]) have the same width frame rails so the perches could be the same. That 361 should be governed around 3600-4000 you wouldn't want to rev that 15" clutch much higher than that. Most of the later stuff wont have a splitter though.

Posted By: Handygun

Re: Gear Ratio & Tire Size Options For A D600?? - 08/13/14 12:42 AM

Perhaps Asian would be a better term today